Xenogeneic tissue, implant tissue from species different than the implanted species, is useful for replacing human organs damaged by pathological or physical injury. Xenografts are used for replacing heart valves, tendons, skin, blood vessels, ligaments, etc.
Xenografts are treated by several processes for crosslinking the predominate collagen to render the xenografts less susceptible to degradative mechanisms of the human system. Xenografts are preserved in sterile solutions, usually a dilute solution of glutaraldehyde or formaldehyde following treatment, during shipment and awaiting Implantation. While the apparatus and methods of this invention are not so limited, the washing of heart valve prostheses will be described to illustrate and exemplify the invention. A typical tissue heart valve prosthesis is made of a porcine heart or of membrane tissue mounted on a stent. The tissue is treated with various reagents to cross-link the collogen, alter the characteristics of the tissue, etc. and is preserved in a glutaraldehyde or formaldehyde or other solution which contains a preservative and/or bacteriostatic compound. For descriptive purposes, glutaraldehyde solutions will be discussed as exemplary, though the particular nature of the solution is not critical to the invention. It is extremely important that all of the glutaraldehyde, formaldehyde or other preservative solutions be removed from the valve before it is implanted in the patient. Some chemical treatments create the risk that some toxic responses will be encountered in sensitive individuals, even after general washing of the xenograft prior to implantation. Frolova, M. A.; Barbarash, L. S.; Gudkova, R. G.; Carpinskaya, B. M., The Effect of Various Preservation Methods on Immunogenicity and Antigenic Composition of Xenogeneic Valve Tissue of the Heart, Byull. Eksp. Biol. Med., Volume No. 3, 1973, pp. 83-86.
The washing step has been tedious, time consuming and must be accomplished immediately before surgery. The general methods of rinsing the xenograft prior to implantation have not substantially decreased the risk of toxic response by completely removing the preservative. The present invention is designed to provide a system for complete washing of valve and graft tissues with a maximum of efficiency and a minimum of inconvenience and time.
SUMMARY OF THE INVENTION
The invention is a system for washing heart valve prosthesis, xenografts and other implants which require extended or repeated washing to remove a preservative and/or to pre-treat the prosthesis immediately before implantation.
The system typically includes a number of disposable containers of saline solution, or other wash solution. Sterile polyethylene or other polymeric containers are readily available and are conveniently used in this invention. Flow of wash solution from the containers controlled by a valve or a series of valves through a sterile filter and then through the wash chamber containing the prosthesis thoroughly washes the prosthesis many times and removes all soluble constituents of the preservative medium. The effluent from the wash chamber passes through a reaction chamber, controlled by suitable valves, which comprises a detection device for determining the presence or absence of preservatives in the effluent wash solution, thus permitting the operator to be certain that the xenograft has been thoroughly washed and that all preservative has been removed. The detection device may include any of several chemical and instrumental analytical systems and apparatus, such as, for example, a photometer, membrane electrode, polarimeter, oxidation-reduction cell, or indicator solution. The specific method for detecting the absence of presence of the preservatives is not critical. For example, an indicator for aldehydes may be metered into a reaction chamber, providing a color change based on the presence of aldehydes. Another sterile filter may be provided in the effluent line as the effluent wash solution is drained to a suitable waste disposable system. These filters assure the continued sterility of the system. The sterile filters can be checked to assure that no bacteria or other organisms have entered into the system.
The flow in the wash chamber is preferably directed to flow over all of the surfaces of the heart valve or graft which is to be washed. The heart valve or other tissue prosthesis can be washed with very little attention, and with a high degree of confidence that the washing is complete.
The wash chamber is preferably designed as a shipping and storage package functioning to preserve as well as wash the heart valve prosthesis. In a preferred form the wash chamber comprises a funnel with specific prosthesis supports designed to support the particular prosthesis in a configuration which will permit the fluid to wash all surfaces and a cap having means configured to direct the flow of the wash solution over the prosthesis. In a preferred form, a filter cloth surrounds the prosthesis and breaks down any jets of wash solution and difuses the flow over the surfaces of the prosthesis. The cap and funnel are constructed and configured to provide a relatively high velocity, low instantaneous volume fluid flow around the valve and through the sewing ring.
The invention is, in its preferred configuration, an integral package functioning as a storage and wash chamber, which may include a built-in recirculating pump to increase the efficiency of the washing and/or treating of the prosthesis. The heart valve prosthesis is placed within the chamber, which is filled with a suitable preservative solution. Seals close the top and bottom conduits of the chamber, which are configured to be connected to tubing, valve, etc. to complete the system. The chamber thus formed by the funnel and cap is enclosed in a heat sealable polyethylene or other polymeric material pouch to provide physical protection, and to serve as a tamper indicator and dust/lint protector and to maintain sterility. The pouch is then, typically, placed in an expanded polystyrene shell for shock protection and to moderate temperature extremes during shipping.
The prosthesis is prepared for implantation by removing the cap seals, draining the storage solution, and connecting the wash chamber to tubes to which are connected to allow the flow of saline solution through the chamber and over the prosthesis. In the preferred embodiment, a built-in recirculating pump, fully prepared to run and supplied with batteries, may be turned on immediately without further preparation. The heart valve prosthesis is maintained in its proper washing configuration in the wash chamber to prevent damage before implantation. The prosthesis is then ready to be implanted without risk of a toxic reaction due to the presence of preservatives. The wash solution may perform the additional function of coating or treating the prosthesis with any desired reagent immediately before the prosthesis is implanted. Some or all of the wash solution may contain the treating reagent. For example, the final wash phases of the process may very desirably include the step of flowing a solution carrying epithelial cells for coating the prosthesis with the epithelial cells immediately before the prosthesis is implanted in the patient.